This invention relates to a spray booth, in which articles are spray-coated with powder.
Such a booth is disclosed in German Offenlegungsschriften Nos. 2 731 123 and 2 809 020. Exhaust-air cleaners mounted on the side walls draw powder-charged air across the inside of the booth and withdraw the air from the booth through filters. The powder removed from the air by the filters precipitates into gutter-like receptacles under the filters and outside the booth. The floor of the booth is a smooth-surfaced chute that slopes down at an angle to its length, in such a manner that the powder that falls on the floor will slip sideways out of the booth into the gutter-like receptacles.
Another booth, disclosed in German Offenlegungsschrift No. 2 945 934, consists of three units, of which only the middle unit constitutes an actual spraying area. The sprayers are mounted on side walls. There is a mesh-covered powder receptacle mounted underneath the booth and extending over its entire area. The floor of the receptacle is fluidized and captures the powder as it falls. Powder-transport lines lead from the receptacle to the sprayer. The two end units are entrance and exit locks that house blowers and exhaust-air filters. The blowers draw powder-charged air along the length of the booth, from within the middle unit, through lateral slits in the end units, and finally, into the filters. Reversing the direction of air flow through the filters causes the powder collected on them to fall to the fluidized floor. The disadvantages of this spray booth are that its length cannot be utilized so that the actual spraying area may be varied and that it takes up too much room. Also, the path of air from the spraying area to the filters in the lock units at each end is long and indirect, necessitating the use of high-output blowers which consume a great deal of power. The powder that drops off the filters cannot be returned to the middle unit continuously, but only in the intervals between spray coating and then only by using a strong countercurrent.
German OFfenlengungsschrift No. 2 946 436 and German Auslegeschrift No. 2 546 920 disclose spray booths in which the exhaust air is drawn down through the floor. The disadvantage of this method is that while the powder should remain around the articles being coated as long as possible, the fall of the powder is instead accelerated.
German Offenlegungsschrift No. 2 835 474 discloses a booth with exhaust-air cleaners immediately under the spray-coating area. All of the falling powder drops onto the filters.
As used herein, "powder" is defined as coating materials with particles ranging in size from powdery to granular. A "fluidized floor" or fluidized surface is defined as one through which a gas, usually air, is blown through a large number of openings to form a cushion that supports the particles of powder. A "spraying station" is defined as any point along the booth at which spray guns can be or are positioned for spray coating.